PSI - Issue 77

João Custódio et al. / Procedia Structural Integrity 77 (2026) 447–456

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João Custódio, et al. / Structural Integrity Procedia 00 (2026) 000–000

3. ASR and DEF effects on concrete Although ASR and DEF are different types of internal swelling reactions, their visible effects on concrete structures are comparable. The main deterioration sign associated to these reactions is cracking, which in unreinforced concrete, is typically characterised by a random crack distribution through the concrete’s surface, known as map cracking, whereas, in reinforced concrete, crack development tends to occur in one or two directions, owing to internal stress restriction provided by the reinforcement. Other relevant effects of ASR and DEF on concrete structures are the closing of expansion joints, the existence of a significant deflection, differential swelling of the concrete around a crack, rupture of reinforcement, disintegration of the concrete, staining of the facings, the presence of pop outs at the bottom of which an aggregate or whitish product is visible, or the appearance of exudations along the cracks. Generally, ASR and DEF cause a very significant reduction of tensile strength and modulus of elasticity, whilst the compressive strength only begins to decrease significantly at high levels of expansion. Although it is common knowledge that concrete's main characteristic is its compressive strength, this belief sometimes overlooks the role of concrete in the performance of reinforced concrete. In fact, beyond durability issues, the microcracks that cause the reduction in tensile strength and elastic modulus affect the delayed behaviour of the structure, not only due to creep and second-order effects, but also in terms of fatigue strength. The local interconnection of cracks can lead to the monolithic response of structural elements being conditioned by these macro defects. Hence, the structural integrity of large concrete structures can be severely compromised by their evolution, ultimately leading to their decommission and demolition. 4. Prevention in new structures Currently, in Europe, there is no specific standard for preventing ASR and DEF in new concrete structures, and each country must rely on national specifications or guide documents. However, EN 206 (CEN, 2013) and EN 12620 (CEN, 2008) state that actions shall be taken to prevent ASR in new structures using procedures of established suitability. Moreover, EN 13670 (CEN, 2009) mentions that if concrete is exposed to high temperature over a specific period in its early life, DEF can occur depending on humidity and concrete mix design. Furthermore, this standard recommends that, unless specified otherwise, the peak temperature of the concrete within a component exposed to a wet or cyclic wet environment shall not exceed 70 °C, unless data is provided to demonstrate that, with the combination of materials used, higher temperatures should have no significant adverse effect on the service performance of the concrete. Nonetheless, these normative documents do not provide any further guidance on the actions that shall be undertaken to prevent or mitigate ASR or DEF in new structures. In Portugal, LNEC Specification E 461:2021 (LNEC, 2021) identifies potentially alkali-silica reactive aggregates, i.e., aggregates that contain forms of silica that may be reactive with alkalis, as well as defines the methodologies for assessing the alkali-reactivity of aggregates and the likelihood that concrete mixtures will develop deleterious expansive reactions (ASR and DEF), and also establishes measures that can be used to prevent the development of deleterious expansive reactions (ASR and DEF)in new concrete structures. In France, guidelines and recommendations have been issued on the prevention and mitigation of the development of deleterious ASR and DEF in new structures, such as (LCPC, 1994), (SETRA, 1996), (LCPC, 2007), (CETMEF, 2008), (Ifsttar, 2017) and (Ifsttar, 2018). Furthermore, the national standard FD P18-464 (AFNOR, 2021) establishes provisions for the prevention of ASR and resulting disorders in structures, including buildings. In the UK, several recommendations exist on ASR, namely the Concrete Society Technical Report TR30 (CS, 1999) and Digest 330 (BRE, 2004a; b; c; d). This Digest, composed of four parts, offers guidance for general concrete applications, particularly detailed guidance on minimising the risk of damaging ASR in new construction (in Part 2), worked examples (in Part 3) and simplified guidance for new construction using aggregates of normal reactivity (in Part 4). Additionally, the Information Paper 1/2002 (BRE, 2002) supplements the guidance given in BRE Digest 330 (BRE, 2004a; b; c; d), and TR 30 (CS, 1999), covering some alternative methods for minimising the risk of damaging ASR in concrete, including the use of some Type II additions (silica fume, fly ash conforming to BS EN 450 (BSI, 2012) and metakaolin) and one type of admixture (lithium salts). British Standards BS 8500-1 (BSI, 2023a) and BS 8500-2 (BSI, 2023b) also provide guidance on preventing ASR in new structures, but they only briefly mention DEF.